Electronic information embedding method and extracting method, electronic information burying apparatus and extracting apparatus, and programs therefor

ABSTRACT

On embedding electronic watermark data in point group data obtained from a three-dimensional measurement, an x-y plane region defining the point group data is divided into a plurality of small regions so that a point group is produced with respect to each of small regions. The coordinate values of each point group are offset with making a barycenter of the point group be an origin point. A discrete Fourier transform is carried out in order to produce a Fourier coefficient sequence, which is modified into a watermarked Fourier coefficient sequence. The inverse discrete Fourier transform is carried out on the watermarked coefficient sequence in order to produce a watermarked complex number sequence. An optimum watermark embedding strength is calculated. On the basis of the embedding strength, the Fourier coefficient sequence is modified to produce a watermarked Fourier coefficient sequence which is is inversely offset into the watermarked point group data.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for managingan original random point group data (three dimensional point group data)which are obtained on the basis of a three dimensional measurement, andmore particularly, to a method and an apparatus for use in embeddingelectronic information as electronic watermark data in the threedimensional point group data in order to prevent an unauthorized usewith respect to the three dimensional point group data which areobtained by measuring the surface of the earth on the basis of the threedimensional measurement using a laser.

BACKGROUND OF THE ART

In general, a pattern having a plurality of fine factors is embedded ina printed matter, in order to prevent falsification or unauthorized use.The unauthorized use is detected in accordance with information, whichis produced by the pattern. Furthermore, information (embeddinginformation) for preventing the unauthorized use is embedded in mapdata, in order to prevent the unauthorized use with respect to the mapdata described in vector form (vector type). In two or three dimensionalmap data described in the vector type, the embedding in formation isembedded in polygons, which form a plane. For example, a method is knownin which the map data is composed of aggregation of triangle polygonseach of which is divided into four triangles. The electronic watermarkdata are embedded as embedding data in a triangle formed between thetriangle polygons (a triangle which does not include vertexes of eachtriangle polygon). By using the above-mentioned method, it is difficultto remove the electronic watermark data without affecting the map datadescribed in the vector type.

On the other hand, disclosure is made in Japanese Patent Publication2001-160897 A about embedding the embedding information for theunauthorized use prevention in the map data described in the vectortype. In the publication, information having an embedding standard layerand an embedding reference layer is inputted to map pictorialinformation representative of a coordinate sequence of layout points ineach object. The information having the embedding standard layer and theembedding reference layer is inputted to layer information which is foruse in managing a type of each object. An embedding reference objectpair is selected which exists in a region having the same meaning andwhose region does not have other objects. An object is selected in whichit is difficult to find out its embedded location, with respect to theembedding reference object. Renewal embedding object information isproduced in accordance with an existence location and/or a shapecharacteristic of the selected object and a renewal object is embeddedon the basis of an embedding density in synchronism with the objectinformation.

Recently, the surface of earth (ground level) is measured by usingso-called laser three-dimensional measurement in order to obtain data ofground level as an original random point group data and to obtain mapdata in accordance with the original random point group data. Moreparticularly, an aircraft irradiates a laser pulse beam towards theground in order to obtain spatial coordinates of the ground level. Inthis event, the spatial position of the aircraft is calculated by usinga GPS reference station positioned on the ground and a GPS receiverinstalled on the aircraft. The attitude of the aircraft is calculated byusing a three-axis gyroscope.

Incidentally, the ground coordinates of each one pulse is produced as x,y, and z coordinates of laser beam reflected point by the irradiatingangle of the laser mirror and the slant distance of the laser mirror, inaccordance with the spatial position and the attitude of the aircraftthat are obtained in the manner described above.

Inasmuch as the ground coordinates obtained in the manner describedabove is merely representative of the random point group data of theground level, it is necessary to process the random point group datainto the map data.

Inasmuch as the original point group data described above are pointgroup data, which are merely dispersed spatially, the original pointgroup data, does not have relationships among one another and does nothave attributes, respectively. In other wards, the original point groupdata are merely representative of x, y, and z coordinates. Accordingly,it is impossible to use the method of embedding the electronic watermarkdata into the above-mentioned vector type map data, with respect to theoriginal point group data. As a result, it is easy to produce the mapdata by the unauthorized use of the original random point group data.

In addition, it is difficult to reproduce the original random pointgroup data in case of embedding the electronic watermark data into theoriginal random point group data in accordance with random numbers,within a predetermined accuracy. Furthermore, it is difficult to preventthe unauthorized use in case of partially thinning out the originalrandom point group data, in order to embed the electronic watermark datainto the original random point group data.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an electronicinformation embedding method, an electronic information embeddingapparatus, and a program each of which is capable of preventingunauthorized use of original random point group data.

It is another object of the present invention to provide an electronicinformation extracting method, an electronic information extractingapparatus, and a program each of which is for use in extracting theelectronic information from the original random point group data intowhich the electronic information is embedded.

According to the present invention, there is provided an electronicinformation embedding method for use in embedding electronic informationas electronic watermark data in original random point group data whichare obtained on the basis of a three dimensional laser measurement. Theelectronic information embedding method is characterized by comprising afirst step of carrying out a discrete Fourier transform with respect tothe original random point group data to produce a Fourier coefficientsequence, a second step of modifying the Fourier coefficient sequence inaccordance with the electronic watermark data to produce a watermarkedFourier coefficient sequence, and a third step of carrying out aninverse discrete Fourier transform with respect to the watermarkedFourier coefficient sequence to produce a watermarked point group dataon the basis of the inverse discrete Fourier transform.

In this case, the first step comprises a fourth step of producing apoint group with respect to each of small regions into which an x-yplane region defining said original random point group data is dividedin a predetermined number, a fifth step of offsetting x and y coordinatevalues of each point group with making a barycenter of the point groupbe an origin point, to convert each point group into an offset pointgroup, and a sixth step of carrying out the discrete Fourier transformwith respect to each of the offset point group to produce the Fouriercoefficient sequence.

In addition, the third step comprises a seventh step of carrying out theinverse discrete Fourier transform with respect to the watermarkedFourier coefficient sequence to produce a watermarked complex sequence,an eighth step of producing an optimum watermark embedding strengthwhich satisfies a tolerance of coordinate error based on watermarking,with respect to the watermarked complex sequence, a ninth step of againmodifying the Fourier coefficient sequence in accordance with theoptimum watermark embedding strength to produce a watermarked Fouriercoefficient sequence, and a tenth step of inversely offsetting thewatermarked Fourier coefficient sequence to produce the watermarkedpoint group data.

Furthermore, there is provided an electronic information extractingmethod of extracting the electronic watermark data from the watermarkedpoint group data which is obtained in the method described above,according to the present invention. The electronic informationextracting method is characterized by comprising an eleventh step ofcarrying out a discrete Fourier transform with respect to the originalrandom point group data and the watermarked point group data withbringing the original random point group data into correspondence withthe watermarked point group data, to produce first and second Fouriercoefficient sequences and a twelfth step of comparing said first Fouriercoefficient sequence with the second Fourier coefficient sequence toextract the electronic watermark data from the first and second Fouriercoefficient sequences.

In this case, the eleventh step comprises a thirteenth step of producinga small region point group with respect to each of small regions intowhich an x-y plane region defining the original random point group datais divided in a predetermined number and a fourteenth step of making asearch for a shortest distance vertex which has a shortest distancebetween a vertex of the small region point group with respect to each ofthe small region point groups, from the watermarked point group data, tobring the original random point group data into correspondence with thewatermarked point group data.

For example, the fourteenth step comprises a fifteenth step of producinga 2-d tree with respect to the watermarked point group data and asixteenth step of setting an inquiry region which is defined by vertexposition of each small region point group and an embedding tolerance, tomake a search for the watermarked point group data included in theinquiry region, from the 2-d tree and to bring the original random pointgroup data into correspondence with the watermarked point group data.

In addition, there is provided an electronic information embeddingapparatus for use in embedding electronic information as electronicwatermark data in original random point group data which are obtained onthe basis of a three dimensional laser measurement, according to thepresent invention. The electronic information embedding apparatus ischaracterized by comprising discrete Fourier transform means forcarrying out a discrete Fourier transform with respect to the originalrandom point group data to produce a Fourier coefficient sequence,modifying means for modifying the Fourier coefficient sequence inaccordance with the electronic watermark data to produce a watermarkedFourier coefficient sequence and watermarked point group data producingmeans for carrying out an inverse discrete Fourier transform withrespect to the watermarked Fourier coefficient sequence to produce awatermarked point group data on the basis of said inverse discreteFourier transform.

In this case, the discrete Fourier transform means comprises dividingmeans for producing a point group with respect to each of small regionsinto which an x-y plane region defining the original random point groupdata is divided in a predetermined number, offset means for offsetting xand y coordinate values of each point group with making a barycenter ofthe point group be an origin point, to convert each point group into anoffset point group, and Fourier coefficient producing means for carryingout the discrete Fourier transform with respect to each of the offsetpoint group to produce the Fourier coefficient sequence.

Furthermore, the watermarked point group data producing means comprisescomplex sequence producing means for carrying out the inverse discreteFourier transform with respect to the watermarked Fourier coefficientsequence to produce a watermarked complex sequence, watermark embeddingstrength producing means for producing an optimum watermark embeddingstrength which satisfies a tolerance of coordinate error based onwatermarking, with respect to the watermarked complex sequence,additional modifying means for again modifying the Fourier coefficientsequence in accordance with the optimum watermark embedding strength toproduce a watermarked Fourier coefficient sequence, and inverse offsetmeans for inversely offsetting the watermarked Fourier coefficientsequence to produce the watermarked point group data.

Furthermore, there is provided an electronic information extractingapparatus for extracting the electronic watermark data from thewatermarked point group data, which are obtained, by the electronicinformation embedding apparatus described above, according to thepresent invention. The electronic information extracting apparatus ischaracterized by comprising Fourier coefficient producing means forcarrying out a discrete Fourier transform with respect to the originalrandom point group data and the watermarked point group data withbringing the original random point group data into correspondence withthe watermarked point group data, to produce first and second Fouriercoefficient sequences and extracting means for comparing the firstFourier coefficient sequence with the second Fourier coefficientsequence to extract the electronic watermark data from the first andsecond Fourier coefficient sequences.

In this case, the Fourier coefficient producing means comprises dividingmeans for producing a small region point group with respect to each ofsmall regions into which an x-y plane region defining the originalrandom point group data are divided in a predetermined number andcorrespondence means for making a search for a shortest distance vertexwhich has a shortest distance between a vertex of the small region pointgroup with respect to each of the small region point groups, from thewatermarked point group data, to bring the original random point groupdata into correspondence with the watermarked point group data.

For example, the correspondence means comprises 2-d tree producing meansfor producing a 2-d tree with respect to the watermarked point groupdata and vertex correspondence means for setting an inquiry region whichis defined by vertex position of each small region point group and anembedding tolerance, to make a search for the watermarked point groupdata included in the inquiry region, from the 2-d tree and to bring theoriginal random point group data into correspondence with thewatermarked point group data.

In addition, there is provided an electronic information embeddingprogram used in a computer on embedding electronic information aselectronic watermark data in original random point group data which areobtained on the basis of a three dimensional measurement, according tothe present invention. The electronic information embedding program ischaracterized by comprising a first procedure of carrying out a discreteFourier transform with respect to the original random point group datato produce a Fourier coefficient sequence, a second procedure ofmodifying the Fourier coefficient sequence in accordance with theelectronic watermark data to produce a watermarked Fourier coefficientsequence, and a third procedure of carrying out an inverse discreteFourier transform with respect to the watermarked Fourier coefficientsequence to produce a watermarked point group data on the basis of theinverse discrete Fourier transform.

In this case, the first procedure comprises a fourth procedure ofproducing a point group with respect to each of small regions into whichan x-y plane region defining the original random point group data isdivided in a predetermined number, a fifth procedure of offsetting x andy coordinate values of each point group with making a barycenter of thepoint group be an origin point, to convert each point group into anoffset point group, and a sixth procedure of carrying out the discreteFourier transform with respect to each of the offset point group toproduce the Fourier coefficient sequence.

In addition, the third procedure comprises a seventh procedure ofcarrying out the inverse discrete Fourier transform with respect to thewatermarked Fourier coefficient sequence to produce a watermarkedcomplex number sequence, an eighth procedure of producing an optimumwatermark embedding strength which satisfies a tolerance of coordinateerror based on watermarking, with respect to the watermarked complexsequence, a ninth procedure of again modifying the Fourier coefficientsequence in accordance with the optimum watermark embedding strength toproduce a watermarked Fourier coefficient sequence, and a tenthprocedure of inversely offsetting the watermarked Fourier coefficientsequence to produce the watermarked point group data.

Furthermore, there is provided an electronic information extractingprogram of extracting the electronic watermark data from the watermarkedpoint group data which is obtained in the manner described above,according to the present invention. The electronic informationextracting program is characterized by comprising an eleventh procedureof carrying out a discrete Fourier transform with respect to theoriginal random point group data and the watermarked point group datawith bringing the original random point group data into correspondencewith the watermarked point group data, to produce first and secondFourier coefficient sequences and a twelfth procedure of comparing thefirst Fourier coefficient sequence with the second Fourier coefficientsequence to extract the electronic watermark data from the first andsecond Fourier coefficient sequences.

In this case, the eleventh procedure comprises a thirteenth procedure ofproducing a small region point group with respect to each of smallregions into which an x-y plane region defining the original randompoint group data is divided in a predetermined number and a fourteenthprocedure of making a search for a shortest distance vertex which has ashortest distance between a vertex of the small region point group withrespect to each of the small region point groups, from the watermarkedpoint group data, to bring the original random point group data intocorrespondence with the watermarked point group data.

For example, the fourteenth procedure comprises a fifteenth procedure ofproducing a 2-d tree with respect to the watermarked point group dataand a sixteenth procedure of setting an inquiry region which is definedby vertex position of each small region point group and an embeddingtolerance, to make a search for the watermarked point group dataincluded in the inquiry region, from the 2-d tree and to bring theoriginal random point group data into correspondence with thewatermarked point group data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view for describing measurement of ground level based ona three-dimensional laser measurement;

FIG. 2 is a flow chart for describing a manner for use in obtainingwatermarked point group from data obtained by the three-dimensionallaser measurement;

FIG. 3 is a flow chart for describing embedding electronic watermark;

FIG. 4 shows a view for illustrating an example of original random pointgroup data; and

FIG. 5 is a flow chart for describing extraction of watermark data.

BEST MODE FOR EMBODYING THE PRESENT INVENTION

Description will be made as regards the present invention with referenceto figures.

Referring to FIG. 1, a three-dimensional measurement is carried out withrespect to earth surface (for example, ground level) at first, onobtaining original random point group data concerned to earth surface.In case where the three-dimensional measurement is carried out withrespect to earth surface, a three-dimensional laser measurement may beused. On carrying out the three-dimensional laser measurement, anaircraft 11 flies over an area (zone) at which original random pointgroup data should be collected. The aircraft 11 has a laser scanner(aircraft installed laser scanner: not shown), a GPS receiver (notshown), and a gyroscope (IMU: not shown).

Referring to FIG. 2 together with FIG. 1, a pulse laser beam isirradiated from the aircraft installed laser scanner towards the ground(ground level) 12, in the three-dimensional laser measurement (step S1).The aircraft 11 receives a reflected pulse from the ground level 12, asa pulse return. The aircraft installed laser scanner measures a distance(z) between the aircraft and the ground level 12 in accordance with atime difference between a time instant of pulse laser beam irradiationand a time instant of pulse return reception, in order to obtaindistance data. Inasmuch as the pulse laser beam is irradiated at apredetermined time interval, the ground level is defined as discretepoints. In this event, a scanning mirror rotates at one axis (which isperpendicular to the flight direction of the aircraft 11), in the laserscanner. The flight direction is another scanning axis so that data isobtained with respect to the ground level. The IMU calculates a laserirradiating angle at each one pulse on the basis of a mirror rotationangle and a mirror inclination angle.

Furthermore, data is obtained with respect to the ground level on theground, using a laser scanner (ground installed laser scanner). In theground installed laser scanner, the scanning mirror has two rotatingaxis so that it is possible to radically obtain the data with respect tothe ground level.

On the other hand, a reference point measurement is carried out inaccordance with a GPS radio wave (step S2). In other wards, the spatialposition of the aircraft 11 is measured by using the GPS receiver, theIMU, and a GPS reference station 13 installed on the ground. After that,scanning point data are converted into geodetic coordinate data on thebasis of data (scanning point data) obtained by the three-dimensionallaser measurement and data obtained by the reference point measurement,in order to obtain the original random point group data (step S3). Inother words, x, y, and z (height H) coordinates are produced whichrepresent laser beam reflected point of the ground level 12, at each onepulse, in order to obtain the original random point group data.

Electronic watermark data are embedded into the above-mentioned originalrandom point group data (step S4) that are outputted as watermarkinformation (data) embedded three-dimensional spatial coordinate pointgroup (step S5). Incidentally, a computer (not shown) carries out thesteps S3 to S5. In other words, the computer comprises at least ageodetic coordinate converting section for carrying out the step S3, anelectronic watermark embedding section for carrying out the step S4, anda watermark point group outputting section for carrying out the step S5.The geodetic coordinate converting section reads the scanning point dataand the reference point measurement data to produce the original randompoint group data.

Referring to FIG. 3, description will proceed to an operation of theelectronic watermark embedding section.

In the example being illustrated, the electronic watermark embeddingsection comprises a small region dividing section, a coordinate offsetsection, a discrete Fourier transform section, a Fourier coefficientsequence modifying section, an inverse discrete Fourier transformsection, an embedding strength automatic adjusting section, and aninverse offset section.

On carrying out an electronic watermark data embedding process, theoriginal random point group data (which will be merely called originalpoint group) V is supplied from the above-mentioned geodetic coordinateconverting section to the small region dividing section. Furthermore,the small region dividing section is supplied with x and y directionsizes D_(x) and D_(y) of each small region, from another inputtingdevice (not shown).

It will be assumed that the original point group V is given by:V={ν _(i)=(x _(i) , y _(i) , z _(i))εR ³|0≦i≦N−1}

-   -   ν_(i) : three dimensional coordinates of vertex, N: the number        of entire vertexes    -   D_(x), D_(y): x and y direction size of divided small region        (normal value D_(x)=100[m], D_(y)=100[m])

At first, the small region dividing section divides the original pointgroup into a plurality of small regions (step A1). As shown in FIG. 4,the original point group V is defined in a rectangular region of x-yplane. The small region dividing section equally divides the rectangularregion into a plurality of small regions A_(a) each of which has thesize (dimension) of D_(x) and D_(y) (equal division), to produce aplurality of point groups V_(a) included in the small regions A_(a),respectively. The point groups V_(a) are supplied to the coordinateoffset section.

$\begin{matrix}{V = {\bigcup\limits_{1 \leq a \leq L_{A}}V_{a}}} & (1)\end{matrix}$

L_(A): the number of entire small regions

Incidentally, a small region having a size less than D_(x) and D_(y) maybe formed at the ends of the rectangular region such as lower and rightsides, when the rectangular region is divided along the x and ydirections. V_(La) will designate a point group in the small regionhaving a size less than D_(x) and D_(y).

The coordinate offset section carries out an offset of x and ycoordinates with respect to the point group of each small region (stepA2). For example, the coordinate offset section converts the x and ycoordinates of the point group V_(a) of each small region into an offsetpoint group V _(a) with making a barycenter of point group V_(a) be anorigin point. As a result, the offset point group V _(a) is given by:V _(a)={ ν _(i)| ν _(i)=ν_(i)−[μ_(ax),μ_(ay),0], ν_(i) εV _(a), 0≦i≦|V_(a)|−1}  (2)

μ_(ax), μ_(ay): x and y coordinates of barycenter of point group V_(a)

$\begin{matrix}{{\mu_{ax} = {\frac{1}{V_{a}}{\sum\limits_{v_{i} = {{({x_{i},y_{i},z_{i}})} \in V_{a}}}x_{i}}}},\mspace{20mu}{\mu_{ay} = {\frac{1}{V_{a}}{\sum\limits_{v_{i} = {{({x_{i},y_{i},z_{i}})} \in V_{a}}}y_{i}}}}} & (3)\end{matrix}$

In case where the absolute value is great in x and y coordinates of theoriginal point group V, it is possible to reduce an influence of errorthat is based on floating-point arithmetic using in an embeddingprocess, by the above-mentioned offsetting process.

The offset point group V _(a) is supplied to the discrete Fouriertransform section and the embedding strength automatic adjustingsection. The small region barycenter μ_(ax) and μ_(ay) is supplied tothe inverse offset section.

The discrete Fourier transform section carries out discrete Fouriertransform (DFT) with respect to the offset point group V _(a) (step A3).In the step A3, the discrete Fourier transform section firstly producesa complex number sequence {ck} given by Equation (4), in accordance withx and y coordinates included in the offset point group V _(a).c _(k) = x _(k) +i y _(k), ( x _(k) , y _(k) ,z _(k))ε V _(a), 0≦k≦|V_(a)|−1  (4)

i:imaginary unit

Secondly, the discrete Fourier transform section carries out discreteFourier transform with respect to the complex number sequence {ck} onthe basis of Equation (5) to produce Fourier coefficient sequence {C₁}.

$\begin{matrix}{{C_{l} = {\sum\limits_{k = 0}^{{V_{a}} - 1}\;{c_{k}\left( {\mathbb{e}}^{{- 2}\pi\;{i/{V_{a}}}} \right)}^{kl}}},{l = 0},1,\cdots\mspace{11mu},{{V_{a}} - 1}} & (5)\end{matrix}$

The Fourier coefficient sequence {C₁} is supplied to the Fouriercoefficient sequence modifying section. The Fourier coefficient sequencemodifying section is further supplied with an electronic watermark databit sequence B and an embedding strength initial value P_(init). TheFourier coefficient sequence modifying section modifies the Fouriercoefficient sequence {C₁} in accordance with the electronic watermarkdata bit sequence B and the embedding strength initial value P_(init)(step A4).

The electronic watermark data bit sequence B is given by:B={b _(m)ε{0, 1}|1<m<N _(b)}

-   -   N_(b): bit length of watermark data    -   p_(init): initial value of watermark embedding strength (normal        value P_(init)=5000)

Using the electronic watermark data bit sequence B={b_(m)ε{0,1}|1≦m≦N_(b)} and the embedding strength initial value P_(init), theFourier coefficient sequence modifying section modifies the Fouriercoefficient sequence {C₁} on the basis of Equation (6), to produce amodified Fourier coefficient sequence {C′₁}.

$\begin{matrix}{{C_{l}^{\prime}} = \left\{ \begin{matrix}{{C_{l}} + p} & \left( {b_{l} = 0} \right) \\{{C_{l}} - p} & \left( {b_{l} = 1} \right)\end{matrix} \right.} & (6)\end{matrix}$

Incidentally, a coefficient C₀ representative of direct currentcomponent is not modified by the watermark data. Therefore, a watermarkbit length which is possible to be embedded into the small region A_(a)becomes |V_(a)|−1. In addition, the value of embedding strength p isdetermined as p←P_(init), on a primary embedding process. The value ofembedding strength p is determined as p←p_(opt), on a secondaryembedding process.

In this event, next rules are used on the basis of a relationshipbetween the watermark bit length N_(b) and the embedding possible bitlength |V_(a)|−1.

i) In case of N_(b)<|V_(a)|−1:

The watermark bits are repeatedly embedded so that the entire Fouriercoefficient C₁, C₂, . . . , C_(|Va|−1) are modified in accordance withthe above-mentioned Equation (6).

i) In case of N_(b)>|V_(a)|−1:

The watermark bits are embedded, using |V_(a)|−1 bits from a head. Otherbits is not embedded.

The modified Fourier coefficient sequence {C′₁}, namely, the watermarkedFourier coefficient sequence {C′₁} is supplied to the inverse discreteFourier transform section. The inverse discrete Fourier transformsection carries out an inverse discrete Fourier transform (IDFT) withrespect to the modified Fourier coefficient sequence {C′₁} (step S5).For example, the inverse discrete Fourier transform section carries outthe inverse discrete Fourier transform given by Equation (7), withrespect to the watermarked Fourier coefficient sequence {C′₁}. As aresult, the inverse discrete Fourier transform section produces acomplex number sequence {c′_(k)} which is modified in accordance withthe electronic watermark.

$\begin{matrix}{{c_{k} = {\frac{1}{V_{a}}{\sum\limits_{k = 0}^{{V_{a}} - 1}{C_{l}^{\prime}\left( {\mathbb{e}}^{2\pi\;{i/{V_{a}}}} \right)}^{kl}}}},{k = 0},1,\cdots\mspace{11mu},{{V_{a}} - 1}} & (7)\end{matrix}$

The complex number sequence {c′_(k)} is supplied to the embeddingstrength automatic adjusting section. The embedding strength automaticadjusting section is supplied with the above-mentioned offset pointgroup V _(a) and an embedding tolerance τ. Taking the embeddingtolerance τ into consideration, the embedding strength automaticadjusting section automatically adjusts the embedding strength (stepA6).

τ: an embedding tolerance of x and y directions (normal value τ=0.3[m])

More particularly, the embedding strength automatic adjusting sectionknows coordinates of watermarked point group data V′_(a) from themodified complex number sequence {c′_(k)} to produce a maximum errorE_({circumflex over (k)}) of the x and y directions, between vertexes ν_(k)=( x _(k), y _(k), z _(k)) (ε V _(a)) of the no embedded point groupV _(a) and vertexes ν′_(k)=( x′_(k), y′_(k), z _(k)) (ε V′_(a)) ofembedded point group V′_(a). The embedding strength automatic adjustingsection calculates a vertex number {circumflex over (k)} which gives themaximum error. The maximum error is given by:

$\begin{matrix}{E_{\hat{k}} = {\max\left( {{\max\limits_{k \in {\lbrack{0,{{V_{a}} - 1}}\rbrack}}\left( {{{\overset{\_}{x}}_{k}^{\prime} - {\overset{\_}{x}}_{k}}} \right)},{\max\limits_{k \in {\lbrack{0,{{V_{a}} - 1}}\rbrack}}\left( {{{\overset{\_}{y}}_{k}^{\prime} - {\overset{\_}{y}}_{k}}} \right)}} \right)}} & (8)\end{matrix}$

It will be assumed that τ is representative of a tolerance (allowablevalue) of vertex coordinate error in x and y directions that occurs onthe basis of embedding. Furthermore, it will be assumed that p_(opt) isrepresentative of an optimum watermark embedding strength whichsatisfies the tolerance. The proportional relationship holds which isgiven by Equation (9).

$\begin{matrix}{\frac{E_{\hat{k}}}{\tau} = \frac{p_{init}}{p_{opt}}} & (9)\end{matrix}$

From Equation (9), the optimum watermark embedding strength p_(opt),which satisfies the tolerance τ of the embedding error is given by:

$\begin{matrix}{p_{opt} = {\frac{\tau}{E_{\hat{k}}}p_{init}}} & (10)\end{matrix}$

The optimum watermark embedding strength p_(opt) is fed back to theFourier coefficient sequence modifying section.

The Fourier coefficient sequence modifying section modifies the Fouriercoefficient sequence on the basis of the optimum watermark embeddingstrength p_(opt) to produce a modified result. The inverse discreteFourier transform section again carries out the inverse discrete Fouriertransform in accordance with the modified result. In other words, theabove-mentioned steps A4 and A5 are again carried out in accordance withthe optimum watermark embedding strength p_(opt) obtained by the mannerdescribed above, in order to produce the electronic watermarked offsetpoint group V′_(a).

The electronic watermarked offset point group V′_(a) is supplied to theinverse offset section. As described above, the inverse offset sectionis supplied with the small region barycenter μ_(ax) and μ_(ay). Theinverse offset section carries out the inverse offsetting with respectto the x and y coordinates to produce watermarked point group V′_(a)(step A7). For example, the inverse offset section carries out aninverse operation of the above-mentioned Equation (2). In other words,the inverse offset section carries out the inverse offsetting on thebasis of Equation (11) to calculate the watermarked point group V′_(a)in accordance with the watermarked point group V′_(a).V′ _(a)={ν′_(i)|ν′_(i)= ν′_(i)+[μ_(ax),μ_(ay), 0], ν′_(i) ε V′ _(a),0≦i≦|V _(a)|−1}  (11)

As described above, the electronic watermark embedding section carriesout processing with respect to each of the small regions to finallyproduce the watermarked point group V′. A watermarked point group outputsection outputs the watermarked point group V′ as watermark informationembedded three-dimensional spatial coordinate point group to a file.

Referring to FIG. 5, description will be made about extracting thewatermark data from the watermarked point group data V′. In the examplebeing illustrated, the computer comprises a watermark data extractingsection which has a point group small region dividing section, a vertexcorrespondence section, a discrete Fourier transform section, and awatermark bit sequence extracting section.

It will be assumed that the original point group V is given by:V={ν _(i)=(x _(i) ,y _(i) ,z _(i))εR ³|0≦i≦N−1}

Furthermore, it will be assumed that the watermarked point group V′ isgiven by:V′={ν′ _(i)=(x′ _(i) ,y′ _(i) ,z′ _(i))εR ³|0≦i≦N−1}

The above-mentioned D_(x) and D_(y) (x and y direction sizes of eachsmall region) and τ (embedding tolerance of x and y directions) areequal to those of the electronic watermark data embedding process.

At first, the point group small region dividing section is supplied withoriginal point group V and the sizes D_(x) and D_(y) of the x and ydirections. The point group small region dividing section divides theoriginal point group V into a plurality of small regions (step A8).

Using the sizes D_(x) and D_(y) of the x and y directions that arespecified in the above-mentioned watermark embedding process, the pointgroup small region dividing section divides the original point group Vinto the small regions to produce a point group V_(a) in each of thesmall regions, in a similar manner described in conjunction with theembedding process.

Incidentally, the watermarked point group V′ is stored without division.

The small region point group V_(a) is supplied to the vertexcorrespondence section. The vertex correspondence section is furthersupplied with the above-mentioned embedding tolerance τ and thewatermarked point group V′. The vertex correspondence section brings thevertexes of the small region point group V_(a) into correspondence withthe vertexes of the watermarked point group V′ to output a small regionwatermarked point group V′_(a) (step A9).

More specifically, the vertex correspondence section makes a search fora vertex which has a shortest distance between a vertex v_(i) (ε V_(a))of the small region point group V_(a) with respect to each small regionpoint group V_(a), from the watermarked point group V′. The vertexcorrespondence section adopts the vertex obtained by the above-mentionedsearch, as a watermarked vertex v′_(i) (ε V′) which corresponds to thevertex v_(i).

In the above-mentioned correspondence, it takes a searching time withthe square of point number to make a search for the watermarked vertexv′_(i) when making a search for the shortest vertex in a round robin,inasmuch as the point group V′ includes a great amount of vertexes. Inthe example being illustrated, the watermark data extracting section mayhave a 2-d tree producing section. The 2-d tree producing section mayproduce a 2-d tree with respect to the watermarked point group V′ in aprevious process (step A10). Instead of the watermarked point group V′,the 2-d tree of the watermarked point group is supplied to the vertexcorrespondence section.

The vertex correspondence section sets a small inquiry region which isdetermined by the position of vertex vi (ε Va) of original point groupand the embedding tolerance τ. The vertex correspondence section makes asearch for watermarked vertex group included in the inquiry region, fromthe 2-d tree at a high speed. In other words, the vertex correspondencesection makes a search for watermarked vertex group included in theinquiry region, from the 2-d tree in the round robin. As a result, it ispossible to efficiently carry out a correspondence processing betweenthe original point group v_(i) (ε V_(a)) and the watermarked vertexv′_(i) (ε V′).

After the vertex correspondence section brings original point groupV_(a) included in the small region, into correspondence with thewatermarked point group V′_(a), the discrete Fourier transform sectioncarries out the DFT with respect to the original point group V_(a) andthe watermarked point group V′_(a) (step A11). For example, the discreteFourier transform section carries out the DFT given by Equations (4) and(5) with respect to the original point group and the watermarked pointgroup corresponding to the original point group, in a similar mannerdescribed in conjunction with the embedding process, in order to producethe Fourier coefficient sequence {C₁} and the watermarked Fouriercoefficient sequence {C′₁}.

The watermark bit sequence extracting section carries out an extractionof electronic watermark data in accordance with the Fourier coefficientsequence {C₁} and the watermarked Fourier coefficient sequence {C′₁}(step A12). More particularly, the watermark bit sequence extractingsection compares the Fourier coefficient sequence {C₁} and thewatermarked Fourier coefficient sequence {C′₁} each of which is obtainedin the manner described above, in order to extract a bit sequence {tildeover (B)}={{tilde over (b)}_(m)ε{0,1}|1≦m≦N_(b)} of the embeddedwatermark data on the basis of Equation (12).

$\begin{matrix}{{\overset{\sim}{b}}_{l} = \left\{ \begin{matrix}0 & \left( {{{C_{l}^{\prime}} - {C_{l}}} \geq 0} \right) \\1 & \left( {{{C_{l}^{\prime}} - {C_{l}}} < 0} \right)\end{matrix} \right.} & (12)\end{matrix}$

As described above, the extracted watermark bit sequence is comparedwith the original watermark bit sequence which is managed, after thewatermark bit sequence extracting section extracts a bit sequence {tildeover (B)}={{tilde over (b)}_(m)ε{0,1}|1≦m≦N_(b)} of the embeddedwatermark data on the basis of Equation (12). On the basis of thecomparison result, judgment is carries out with respect to whether ornot the watermarked point group data are produced from the originalpoint group data.

Application Possibility on the Industry

It is possible to prevent the unauthorized use of the original randompoint group data in the present invention inasmuch as the electronicwatermark data embedded into the original random point group data, asdescribed above. Furthermore, it is possible to judge whether or not thewatermarked point group data are produced from the original random pointgroup data in accordance with the comparison result, inasmuch as theelectronic watermark data are extracted from the watermarked point groupdata to be compared with the original electronic watermark data whichare managed, as described above. In other words, it is possible to judgean identity of the original random point group data.

1. An aerial electronic map information creation processing method forembedding predetermined electronic map information in measured geodeticcoordinate data of point group state as electronic watermark data, inwhich an aircraft installed with a laser scanner, a GPS receiver, and agyroscope are allowed to fly over an area to collect original randompoint data of the area, said laser scanner being installed such that anaxis of rotation of a scanning mirror of said laser scanner isperpendicular to direction of flight of said aircraft and direction offlight of said aircraft coincides with another scanning line of saidscanning mirror, said GPS receiver carrying out reference pointmeasurement is according with a GPS radio wave, a laser irradiatingangle of every pulse of laser beam irradiated from the laser scannerbeing obtainable from said gyroscope; 3-dimensional data of ground levelare measured by the irradiation of the pulse laser beam to the groundfrom said laser scanner; and said geodetic coordinate data of irregularpoint group state consisting of three coordinates (x, y, z) are obtainedby converting said 3-dimensional data of the ground level into saidgeodetic coordinate data based on spatial position data of the aircraftobtained by said reference point measurement and said laser irradiatingangle obtained by said gyroscope, comprising the steps of: a first stepof carrying out a discrete Fourier transform with respect to factors ofx and y coordinate values extending from said geodetic coordinate dataof a point group state to obtain data, which are vertexes arranged asCk=xk+jyk in one dimension, in order to produce a one dimensionalcomplex Fourier coefficient sequence; a second step of modifying saidFourier coefficient sequence in accordance with said electronicwatermark data to produce a watermarked Fourier coefficient sequence;and a third step of carrying out an inverse discrete Fourier transformwith respect to said watermarked Fourier coefficient sequence to producea watermarked geodetic electronic data on the basis of said inversediscrete Fourier transform.
 2. An aerial electronic map informationcreation processing method as claimed in claim 1, wherein said firststep comprises: a fourth step of inputting a region of small sizecorresponding to an area into which an x-y plane region defining saidgeodetic coordinate data is divided in a predetermined number; a fifthstep of offsetting x and y coordinate values of each point group withmaking a barycenter of said point group be an origin point, to converteach point group into an offset point group; and a sixth step ofcarrying out the discrete Fourier transform with respect to each of saidoffset point group to produce the Fourier coefficient sequence.
 3. Anaerial electronic map information creation processing method as claimedin claim 2, wherein said third step comprises: a seventh step ofcarrying out the inverse discrete Fourier transform with respect to saidwatermarked Fourier coefficient sequence to produce a watermarkedcomplex sequence; an eighth step of calculating an optimum watermarkembedding strength which is proportional to a tolerance of coordinateerror based on watermarking, with respect to said watermarked complexsequence; a ninth step of again modifying the Fourier coefficientsequence in accordance with said optimum watermark embedding strength toproduce a watermarked Fourier coefficient sequence; and a tenth step ofinversely offsetting said watermarked Fourier coefficient sequence toproduce said watermarked point group data.
 4. An electronic informationextracting method of extracting said electronic watermark data from saidwatermarked point group data, which is obtained by the aerial electronicmap information creation processing method, as claimed in claim 3,comprising: an eleventh step of carrying out a discrete Fouriertransform with respect to said geodetic coordinate data and saidwatermarked point group data with vertexes in both groups correspondingto each other, in order to produce first and second Fourier coefficientsequences; and a twelfth step of comparing said first Fouriercoefficient sequence with said second Fourier coefficient sequence toextract said electronic watermark data from said first and secondFourier coefficient sequences.
 5. An electronic information extractingmethod as claimed in claim 4, wherein said eleventh step comprises: athirteenth step of dividing an x-y plane region defining said geodeticcoordinate data into small regions of a size which is the same as theembedded electronic watermark; and a fourteenth step of making a searchfor a shortest distance vertex which has the shortest distance between avertex of the small region point group with respect to each of saidsmall region point groups, from said watermarked point group data, tobring said geodetic coordinate data into correspondence with saidwatermarked point group data.
 6. An electronic information extractingmethod as claimed in claim 5, wherein said fourteenth step comprises: afifteenth step of producing with respect to said watermarked point groupdata, a 2-d tree which is a binary tree structure for managing thewatermarked point group data (x, y) with respect to said watermarkedpoint group data; and a sixteenth step of setting an inquiry regionwhich is defined by vertex position of each small region point group andan embedding tolerance, to make a search for said watermarked pointgroup data included in said inquiry region, from said 2-d tree and tobring said geodetic coordinate data into correspondence with saidwatermarked point group data.
 7. An aerial electronic map informationcreation processing apparatus for converting 3-dimensional data of theground level obtained by use of a laser scanner installed in an aircraftinto a geodetic coordinate data of point group state consisting of threecoordinates (x, y, z) and embedding predetermined electronic mapinformation in measured geodetic coordinate data of point group state aselectronic watermark data, comprising: an aircraft installed with alaser scanner, a GPS receiver, and a gyroscope, said laser beinginstalled such that an axis of rotation of a scanning mirror of saidlaser scanner is perpendicular to a direction of flight of said aircraftand a direction of flight of said aircraft coincides with anotherscanning line of said scanning mirror, said GPS receiver carrying outreference point measurement in accordance with a GPS radio wave, a laserirradiating angle of every pulse of laser beam irradiating from saidlaser scanner being obtainable from said gyroscope; a geodeticcoordinate converting means for obtaining geodetic coordinate data ofirregular point group state consisting of three coordinates (x, y, z) byconverting 3-dimensional data of ground level measured by irradiatingthe pulse laser beam to the ground from said laser scanner into ageodetic coordinate data based on spatial position data of the aircraftobtained by said reference point measurement and said laser irradiatingangle obtained by said gyroscope; an electronic watermark embeddingmeans for producing a watermarked geodetic electronic data by carryingout a discrete Fourier transform with respect to factors of x and ycoordinate values extracted from said geodetic coordinate data of apoint group data, which are vertexes arranged as Ck=xk+jyk in onedimension, in order to produce a one dimensional complex Fouriercoefficient sequence, modifying said Fourier coefficient sequence inaccordance with said electronic watermark data to produce a watermarkedFourier coefficient sequence, and carrying out an inverse discreteFourier transform with respect to said watermarked Fourier coefficientsequence on the basis of said inverse discrete Fourier transform; and anoutput means for outputting said watermarked geodetic electronic data.8. An aerial electronic map information creation processing apparatus asclaimed in claim 7, wherein said discrete Fourier transform meanscomprises: inputting means for inputting a region of small sizecorresponding to each of a plurality of small regions into which an x-yplane region defining said geodetic coordinate data is divided in apredetermined number; offset means for offsetting x and y coordinatevalues of each point group with making a barycenter of said point groupbe an origin point, to convert each point group into an offset pointgroup; and Fourier coefficient producing means for carrying out thediscrete Fourier transform with respect to each of said offset pointgroup to produce the Fourier coefficient sequence.
 9. An aerialelectronic map information creation processing apparatus as claimed inclaim 8, wherein said watermarked point group data producing meanscomprises: complex number sequence producing means for carrying out theinverse discrete Fourier transform with respect to said watermarkedFourier coefficient sequence to produce a watermarked complex numbersequence; watermark embedding strength calculating means for calculatingan optimum watermark embedding strength which is proportional to atolerance of coordinate error due to watermarking, with respect to saidwatermarked complex number sequence; additional modifying means foragain modifying the Fourier coefficient sequence in accordance with saidoptimum watermark embedding strength to produce a watermarked Fouriercoefficient sequence; and inverse offset means for inversely offsettingsaid watermarked Fourier coefficient sequence to produce saidwatermarked point group data.
 10. An electronic information extractingapparatus for extracting said electronic watermark data from saidwatermarked point group data, which is obtained by the An aerialelectronic map information creation processing apparatus, as claimed inclaim 7, comprising: Fourier coefficient producing means for carryingout a discrete Fourier transform with respect to said geodeticcoordinate data and said watermarked point group data by bringingvertexes in said geodetic coordinate data into correspondence withvertexes in said watermarked point group data, to produce first andsecond Fourier coefficient sequences; and extracting means for comparingsaid first Fourier coefficient sequence with said second Fouriercoefficient sequence to extract said electronic watermark data from saidfirst and second Fourier coefficient sequences.
 11. An aerial electronicmap information creation processing apparatus as claimed in claim 10,wherein said Fourier coefficient producing means comprises: dividingmeans for dividing an x-y plane region defining said geodetic coordinatedata into small regions of a size which is the same as the embeddedelectronic watermark; and correspondence means for making a search for ashortest distance vertex which has a shortest distance between a vertexof the small region point group with respect to each of said smallregion point groups, from said watermarked point group data, to bringsaid geodetic coordinate data into correspondence with said watermarkedpoint group data.
 12. An aerial electronic map information creationprocessing apparatus as claimed in claim 11, wherein said correspondencemeans comprises: 2-d tree producing means for producing with respect tosaid watermarked point group data, a 2-d tree which is a binary treestructure for managing the watermarked point group data (x,y) withrespect to said watermarked point group data; and vertex correspondencemeans for setting an inquiry region which is defined by vertex positionof each small region point group and an embedding tolerance, to make asearch for said watermarked point group data included in said inquiryregion, from said 2-d tree and to bring said geodetic coordinate datainto correspondence with said watermarked point group data.